The 18th century telescope above, found in an excavation in Amsterdam,
is quite unusual: it's made of bone.

Ranging in length from roughly 3 to 5 inches (80 to 140 millimeters),
the telescopes were made using cattle metatarsal bone. "This particular
bone of cow, the metatarsal bone, is actually quite straight and round,"
Marloes Rijkelijkhuizen, of the Amsterdam Archaeological Centre at the
University of Amsterdam, told LiveScience."It's a nice shape to
make these telescopes from, it's straight and (has a) very round narrow
cavity."